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arXiv:0911.3868 · Physical Review A

Ultrabright omnidirectional collective emission of correlated photon pairs from atomic vapors

Yu Huang, M. G. Moore

Published Mar 8, 2010• 1 citation
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Abstract

Spontaneous four-wave mixing can generate highly correlated photon pairs from atomic vapors. We show that multiphoton pumping of dipole-forbidden transitions in a recoil-free geometry can result in ultrabright pair emission in the full $4\ensuremath{\pi}$ solid angle, while strongly suppressing background Rayleigh scattering and associated atomic heating, Such a system can produce photon pairs at rates of $~10$${}^{12}$ per second, given only moderate optical depths of $10\ensuremath{-}100$, or alternatively, the system can generate paired photons with subnatural bandwidths at lower production rates. We derive a rate-equation based theory of the collective atomic population and coherence dynamics and present numerical simulations for a toy model, as well as realistic model systems based on $^{133}\mathrm{Cs}$ and $^{171}\mathrm{Yb}$ level structures. Last, we demonstrate that dark-state adiabatic following electromagnetically induced transparency and/or time-scale hierarchy protects the paired photons from reabsorption as they propagate through the optically thick sample.

DOI
10.1103/physreva.81.033807

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Spontaneous four-wave mixing can generate highly correlated photon pairs from atomic vapors. We show that multiphoton pumping of dipole-forbidden transitions in a recoil-free geometry can result in ultrabright pair emission in the full 4\ensuremathπ4\ensuremath{\pi}4\ensuremathπ solid angle, while strongly suppressing background Rayleigh scattering and associated atomic heating, Such a system can produce photon pairs at rates of ~10$${}^{12} per second, given only moderate optical depths of 10\ensuremath−10010\ensuremath{-}10010\ensuremath−100, or alternatively, the system can generate paired photons with subnatural bandwidths at lower production rates. We derive a rate-equation based theory of the collective atomic population and coherence dynamics and present numerical simulations for a toy model, as well as realistic model systems based on 133Cs^{133}\mathrm{Cs}133Cs and 171Yb^{171}\mathrm{Yb}171Yb level structures. Last, we demonstrate that dark-state adiabatic following electromagnetically induced transparency and/or time-scale hierarchy protects the paired photons from reabsorption as they propagate through the optically thick sample.
We propose a novel `butterfly' level scheme to generate highly correlated photon pairs from atomic vapors. With multi-photon Doppler-free pumping, background Rayleigh scattering is dipole-forbidden and collective emission is permitted in all directions. This results in usable pairs generated simultaneously in the full 4π4π4π solid angle. Collecting these pairs can produce photon pairs at a rate of ∼1012\sim 10^{12}∼1012 per second, given only moderate ensemble sizes of ∼106\sim 10^6∼106 atoms.
Tunable Rydberg interactions in cold atoms can be used to generate strongly correlated photon pairs through a spontaneous four-wave-mixing process in which all driving fields are allowed to work on resonance. The scheme relies on electromagnetically induced transparency and an imbalanced dark state with most atoms trapped in a ground state and a weakly populated Rydberg state. We show in particular that the combination of these two effects results in negligible linear absorption and Raman gain at the Stokes and anti-Stokes frequencies of generated photon pairs, while the nonlocal (Rydberg) nonlinearities contribute significantly to the enhancement of photon-pair generation rates and cross correlations at very low pump strengths and optical depths.
Driven by the desire of narrow-band photon pairs source, in this Mphil thesis work, we demonstrate the generation of photon pairs with controllable coherence time up to 1.72 microseconds, using spontaneous four-wave mixing with electromagnetically induced transparency in a laser-cooled atomic ensemble with an optical depth (OD) as high as 130. At such a high OD, we find that the pump laser intensity profile has a significant effect on the time-frequency entangled two-photon waveform. We also confirm the quantum particle nature of heralded narrow-band single photons generated from this source.
The pairing ratio, a crucial metric assessing a biphoton source's ability to generate correlated photon pairs, remains underexplored despite theoretical predictions. This study presents experimental findings on the pairing ratio, utilizing a double- Λ spontaneous four-wave mixing biphoton source in cold atoms. At an optical depth (OD) of 20, we achieved an ultrahigh biphoton generation rate of up to 1.3 × 10 7 per second, with a successful pairing ratio of 61%. Increasing the OD to 120 significantly improved the pairing ratio to 89%, while maintaining a consistent biphoton generation rate. This achievement, marked by high generation rates and robust biphoton pairing, holds great promise for advancing efficiency in quantum communication and information processing. Additionally, in a scenario with a lower biphoton generation rate of 5.0 × 10 4 per second, we attained an impressive signal-to-background ratio of 241 for the biphoton wavepacket, surpassing the Cauchy-Schwarz criterion by approximately 1.5 × 10 4 times. Published by the American Physical Society 2024
The generation of nonclassical photon pairs with a long coherence time is key for applications that range from fundamental to quantum communication and metrology. Spontaneous four-wave mixing with electromagnetically induced transparency has been demonstrated as one of the most efficient methods; however, narrowing the bandwidth and producing photon pairs with a temporal length beyond 1 μs remains a technical challenge due to noise considerations and the need for cold atoms with a high optical depth (OD). In this work, we demonstrate the generation of narrowband photon pairs with a controllable coherence time up to 1.72 μs in a laser-cooled atomic ensemble with an OD as high as 130. At such a high OD, we find that the pump laser field spatial profile has a significant effect on the time–frequency entangled two-photon waveform. We also confirm the quantum particle nature of heralded narrowband single photons generated from this source.
Superradiant biphoton emission from atomic ensembles provides a powerful route to generating highly correlated quantum light, yet its microscopic physical origin has remained incompletely understood. In particular, it is often unclear how collective enhancement, spontaneous emission, and vacuum fluctuations jointly give rise to both paired biphoton generation and unavoidable unpaired background within a single, self-consistent framework. Here we present a fully quantum microscopic theory within a unified Heisenberg--Langevin--Maxwell framework that explicitly incorporates dissipation and quantum noise, thereby revealing the microscopic origin of superradiant biphoton emission in atomic ensembles. The theory provides a consistent description of parametric gain and unpaired noise within the same open-quantum-system framework and applies to both Doppler-free cold atomic ensembles and Doppler-broadened warm vapors. In the high-optical-depth regime, the coupled propagation equations admit analytical solutions, under which the biphoton dynamics rigorously reduce to an effective collective two-level emission process. Within this limit, the biphoton correlation time and spectral properties are shown to obey closed-form scaling relations governed by optical depth and excited-state decoherence. Our results establish a unified microscopic picture of superradiant biphoton generation and clarify the fundamental role of vacuum fluctuations and dissipation in setting the brightness, pairing efficiency, and temporal structure of atomic biphoton sources, with direct relevance to quantum networking and atomic quantum interfaces.